Overfishing imperils ocean life, study says

OCEANS

Jane Kay, Chronicle Environment Writer

Published
4:00 am PST, Tuesday, March 3, 2009

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The stars of the ocean - bluefin tuna, salmon, whales and seabirds - suffer from dwindling food supplies as a result of heavy fishing driven by the demands of fish farms and climate change, according to a study released Monday.

Seven of the world's 10 largest commercial fisheries include small fish such as herring, anchovy, pollock, mackerel and whiting, which support the vast ocean web of big fish, marine mammals and birds, said the study by Oceana, a worldwide environmental group.

The loss of food at the bottom of the ocean food chain harms a range of species, resulting in malnutrition, death of offspring or disruption in migration and breeding patterns, Margot Stiles, lead author and Oceana marine biologist, said Monday.

"These fish may be small. They're not glamorous. But they do all of the work in the ocean," Stiles said. "They're the foundation of the food web. Without them, we would lose the things we really care about - the seabirds, whales, tuna and salmon."

Most small prey, or forage fish, are being caught at maximum levels or are currently overexploited, the study said.

Oceana and another group, Ocean Conservancy, are asking for catch limits that would protect existing fisheries. They also want prohibitions on starting new fisheries of prey species.

Fish farms, known as aquaculture, are overtaking commercial fishing as the prime supply of the world's seafood, the U.N. report said.

The Oceana study, entitled, "Hungry Oceans: What Happens When the Prey Is Gone," focuses on three threats:

-- Overfishing of prey species are going unregulated, including immense stores of squid and krill. Whole schools of fish that feed tuna, whales and other long-lived animals and drive migrations are caught in nets, particularly by industrial fishing vessels.

-- Fish farms are driving the need for small species, which are turned into oil or feed. They use more of the ocean's protein than they produce. An estimated 4 to 11 pounds of prey fish are consumed to grow 1 pound of farmed salmon.

-- Warming ocean temperatures in the past century - and projected to rise in the coming decades - affect sea life survival. Changes in temperature and prevailing currents may sweep away newly hatched eggs and larvae, and hurricanes can wipe out a generation of larval fish.

Climate change also interferes with the timing of life cycles. The food for seabirds and salmon, for example, must be available when they need it. If not, seabirds don't reproduce or their offspring die, and salmon don't survive when they get to the ocean.

Oceana has lobbied for bans on commercial fishing of krill in the Antarctica, Japan and British Columbia and the Gulf of St. Lawrence in Canada.